SELECT...FOR UPDATE in Phalcon

I am using phalcon to develop our backend supporting for a mobile application. Because of bugs in early phalcon version, we workaround by a solution is adding PURE query between Phalcon ORM code lines. Ex:

Does the transaction began after this code line?
$transaction = $transactionManager->get();

or we need to start it manually
$transaction->begin();

Because follow this article the locked rows just be unlocked in case the transaction is committed. So we have to begin the transaction before execute "SELECT FOR UPDATE" and then commit (or rollback) to unlock them